Abstract. Anisotropy of upper mantle physical properties results from lattice preferred orientation (LPO) of upper mantle minerals, in particular olivine. We use an anisotropic viscoplastic selfconsistent (VPSC) and an equilibrium-based model to simulate the development of olivine LPO and, hence, of seismic anisotropy during deformation. Comparison of model predictions with olivine LPO of naturally and experimentally deformed peridotites shows that the best fit is obtained for VPSC models with relaxed strain compatibility. Slight differences between modeled and measured LPO may be ascribed to activation of dynamic recrystallization during experimental and natural deformation. In simple shear, for instance, experimental results suggest that dynamic recrystallization results in further reorientation of the LPO leading to parallelism between the main (010)[ 100] slip system and the macroscopic shear. Thus modeled simple shear LPOs are slightly misoriented relative to LPOs measured in natural and experimentally sheared peridotires. This misorientation is higher for equilibrium-based models. Yet seismic properties calculated using LPO simulated using either anisotropic VPSC or equilibrium-based models are similar to those of naturally deformed peridotRes; errors in the prediction of the polarization direction of the fast S wave and of the fast propagation direction for P waves are usually < 15 ø. Moreover, overestimation of LPO intensities in equilibrium-based and VPSC simulations at high strains does not affect seismic anisotropy estimates, because these latter are weakly dependent on the LPO intensity once a distinct LPO pattern has been developed. Thus both methods yield good predictions of development of upper mantle seismic anisotropy in response to plastic flow. Two notes of caution have nevertheless to be observed in using these results: (1) the dilution effect of other upper mantle mineral phases, in particular enstatite, has to be taken into account in quantitative predictions of upper mantle seismic anisotropy, and (2) LPO patterns from a few naturally deformed peridotRes cannot be reproduced in simulations. These abnormal LPOs represent a small percent of the measured natural LPOs, but the present sampling may not be representative of their abundance in the Earth's upper mantle.

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On the basis of polycrystalline theory describing the plasticity in olivine and enstatite, the flow in a convection cell has been simulated using a finite element formulation. The spatial variations in anisotropic properties are computed from the textures that evolve with the flow. A kinematically constrained equilibrium‐based assumption is used to partition the macroscopic deformation among crystals within an aggregate. We model the convection for one specific cell geometry and two sets of boundary conditions. A complete map of textures throughout the cell is obtained. The textured convection cell is structurally very heterogeneous and textures along streamlines do not correlate with the finite strain. The results of the simulations indicate that during up welling a strong texture develops rapidly. It convects during spreading and is attenuated during subduction. Results are compared with features of the upper mantle. In our predictions the pattern of preferred orientation during spreading is inclined to the flow coordinates due to deformation by simple shear. This is contrary to Hess' [1964] intuition that (001) slip planes of olivine orient themselves parallel to the flow planes, yet the pattern is consistent with natural fabric data. Significant differences are observed as a function of depth within the cell. The variations in the p wave velocities in this textured model mantle are analyzed and correspond well with observed seismic data.

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International audienceHot tearing is an unacceptable defect found in products and parts obtained by solidification processes such as ingot and continuous casting. It consists of the development of cracks during solidification, in regions that are not completely solidified, more precisely, in areas of mushy zones with a high fraction of solid (typically 0.9 and beyond), when the material undergoes deformations associated with tensile stress. In this study, two hot tearing tests have been studied in order to evaluate the predictive capability of several macroscopic criteria published in the literature. The first test is a new test specifically designed for constrained shrinkage by the present authors, while the second test is an ingot bending test developed in the 1980s. For both tests, a thermal-mechanical analysis is performed, in order to provide the key variables for the different selected criteria. A comparison with experimental results allows us to make a critical assessment of those criteria regarding their ability to predict crack occurrence. The criterion initially proposed by Won et al.[7] has been found to be the best suited for the prediction of solidification cracking. Because this criterion is essentially based on the "brittle temperature range," (BTR) critical considerations regarding nonequilibrium solidification have led to suggest an extension of this criterion. This new macroscopic criterion improves the prediction capacity

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